Can you drink alcohol during a fast?
I assure you I’d love the answer to be yes. As a person who practices intermittent fasting once or twice a week, I can tell you that there have been days were I’ve considered breaking a fast solely for a nice pint of Guinness. It doesn’t happen often, but when it does, I will think of every excuse in the book outlining why I should be able to have a drink.
Usually I go with the ‘”because it’s good for you” argument. Then my brain hits me with the counterargument of, “Better than fasting?”
Darn brain always trumps me.
But what actually happens when you do consume alcohol in the fasted state? Is it detrimental to the fat loss we expect from intermittent fasting?
To start a review of alcohol and fasting we need to know two basic things: what happens when we ingest alcohol, and where does it go after we ingest it?
After drinking alcohol, it is readily absorbed by the gastrointestinal tract. About 20% of the absorption of alcohol takes place by passive diffusion through the stomach wall with the rest absorbed through the duodenum and the walls of the small intestine [Norberg A, 2003].
Once the alcohol has been absorbed it is slowly eliminated. This occurs primarily through metabolism, basically it is burned as a fuel. A super small amount of alcohol gets excreted unchanged in the breath (0.7%), sweat (0.1%), and urine (0.3%) [Holford NH, 1997].
Here’s another fun fact: according to Wikipedia (who’s never wrong), the average human digestive system produces approximately 3 grams of ethanol per day (a little less than a third of a beer)… completely irrelevant to an article on intermittent fasting and alcohol, but interesting nonetheless.
However as I said, the point of this isn’t a complete review of the health benefits and metabolism alcohol.
Truthfully, this article came about because of a study titled “Effect of Moderate White Wine Consumption on Serum IgA and Plasma Insulin under fasting conditions”.
In this trial, 5 non-alcoholic men were asked to fast for 6 hours then consume 40 grams of alcohol in the form of medium dry white wine over a 3-hour period.
(To give you an idea, that’s just a little under three “super-sized” (9 oz.) glasses of wine.)
It turns out that this amount of alcohol intake did not raise insulin levels above the fasting levels (stayed below 10 uU/ml)[Kokavec A, 2006]. Pretty cool. Even cooler is that this finding is in line with several other studies. Turns out, alcohol even at these levels doesn’t have much influence on insulin levels [Hawkins R, 1972].
Now, since most people relate insulin levels to fat loss or fat storage, I understand why you might be thinking “HOLY CRAP, PILON JUST SAID I CAN HAVE 3 GLASSES OF WINE DURING MY FAST!!!”
Not so fast.
If you’ve read Eat Stop Eat (and I hope you have) then you know there’s more to fat burning than just insulin. We also have to look at growth hormone (GH).
Luckily, research on acute intake of alcohol and its impact on growth hormone has been conducted. Unfortunately the results are… well… equivocal.
In a trial completed in 1971, 11 healthy men were fed roughly 80 grams of alcohol after an overnight fast. This is the equivalent of drinking a little more than a bottle of wine or about 8 beers.
Following the ingestion of the alcohol, growth hormone levels rose well above normal levels. Within 3 hours after consuming the alcohol their blood free fatty acids (FFA) levels began to fall below normal fasting levels. Interestingly, blood glucose levels remained constant during the 3 hours of measurement [Bellet S, 1971].
This study is a little tricky, since that is a fairly high dose of alcohol. In all honesty, I’d hope that nobody is wondering if they can drink an entire bottle of wine during their fast.
In fact, it could be suggested that the increase in GH was a stress response from the fact that these gentlemen were more than likely intoxicated from this amount of wine, which was consumed fairly quickly, and in the morning.
Regardless, it would seem that with an increase in GH and a decrease in insulin we just might be able to get away with having a couple drinks during our fasts (YES!). Remember from Eat Stop Eat, the key markers of a fasted state are elevated GH and decreased Insulin.
However, it is also well known that both the acute and chronic intake of alcohol alters normal sleep patterns. Typically suppressing rapid eye movement and increasing slow wave sleep, with the magnitude of these changes being directly related to blood alcohol levels [Yules RB, 1966]. I find this to be interesting because it is also well known that nighttime growth hormone secretion is related to the appearance of slow wave sleep.
So we look to another study that examined the effects of a pre-bed drink in 5 adult males. In this trial fasted men consumed 0.8 grams per kilogram of body weight of alcohol prior to sleep (For a 170 pound guy this is about 60ish grams of alcohol, that is about 6 beers or 4 nine-ounce glasses of wine (these are BIG glasses).
As expected blood alcohol levels rose and then returned to baseline levels between 4-6 hours later. But the interesting thing is what happened to their sleep patterns.
REM sleep was decreased, slow wave increased. Not only was sleep perturbed (science talk for messed-up) but the alcohol intake significantly decreased the GH peak associated with slow wave sleep by an almost 70% reduction.
This is a pretty significant alteration in GH levels. It’s also more consistent with other studies finding even moderate acute doses of alcohol can block or blunt various GH responses in the body [Prinz PN, 1980].
So insulin stays low, but GH seems to be blunted unless the intake of alcohol is on the extreme side.
Interesting, but both insulin and GH are what we call “surrogate endpoints” we’re really concerned with what is happening to them as much as we are our true endpoint: fat burning.
Luckily, there’s a study to address this issue.
In study published in 1999, eight healthy men were asked to drink 24 grams of alcohol after a 12-hour fast. Right away I can say this study is a bit more applicable to our situation since this amount of alcohol is what is found in roughly 2 beers, 2 normal glasses of wine, or two 1.5 ounce shots of hard liquor… a much more realistic intake for a casual drinker than trying to drink 6-8 beers during a fast.
In this study, after ingestion of alcohol lipolysis (fat being released from your body fat stores) and fat oxidation (fat being burned as a fuel) plummeted, representing a ~70% decrease in fat burning. Carbohydrate oxidation did not change, but total energy expenditure increased (their metabolic rate went up)[Siler SQ, 1999].
To summarize: a rather normal dose of alcohol caused a decrease in fat burning, no change in carbohydrate burning, and a slight increase in overall calorie burning in men who were in the fasted state.
So the question remains. If metabolic rate increases, glucose oxidation stayed the same, and fat burning decreased… what the heck were they burning?
Turns out the answer is the alcohol… sort of.
The alcohol we consume gets converted into something called acetaldehyde and then into acetate. We can handle acetate, but if we drink too much too quickly, the enzymes responsible for this conversion can’t keep up and the acetaldehyde begins to spill over and can lead to damage and toxic effects. So it makes sense that as much as 77% of the alcohol you ingest becomes blood acetate and that we are well equipped to dispose of this acetate [Manzo-Avalos S, 2010].
The primary fate of circulating acetate is oxidation. In other words it gets burned as a fuel, eventually being metabolized to CO2 in heart, skeletal muscle, and even brain cells. Yes, even your brain is able to switch over and use acetate as a fuel if it’s present in your blood stream.
The rough translation of this is: if acetate it present in your blood it will get used in priority over fat or carbohydrate and protein.
In fact, blood acetate is such a priority that it’s mere presence can decrease lipolysis by ~50%, even when you are in the fasted state [Crouse JR, 1968]
And this is what happens when you drink during your fast. It’s not that you will gain more fat (unless you are drinking excessively), but you will stop releasing body fat, stop burning body fat, and burn acetate instead. This occurs without any change in insulin levels.
So sadly, it seems the answer is that you cannot drink during your fasts without diminishing your fat burning abilities. Luckily, with Eat Stop Eat-style fasts you only fast once or twice a week. Leaving 5 or 6 days were you can have a drink you choose. Heck, I even recommend easy diet hacks that use alcohol as a way to lose weight.
NOTE: I find it odd that ALL of this research was conducted on men. We know that amount of ethanol metabolized by the stomach differs by sex [Frezza M, 1990], but I see no reason why this would exclude women from the “no drinking during a fast” rule.